Casting magnesium and alloys therefor



Patented Au 12, 1930 UNITED. STATES PATENT OFFICE HORACE KELLEY, 0F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, OF- MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN CASTING MAGNESIUM AND ALLOYS THEREFOR No Drawing}.

While the present improvements relate more particularly to the casting of magnesium and so-called light metal alloys in which magnesium is the predominant Constituent, it will be understood that the improved method and apparatus involved are equally adaptable for the casting of any similar, readily oxidizable metal. The difiicultiesencountered in melting and handling in molten state, magnesium or an alloy largely composed of this metal are well known and these difficulties are still presentwhen it is attempted to introduce such metal into a mold in any process of casting. For example, when sand castings are made in the ordinary way by simply pouring the molten magnesium or light alloy metal containing magnesium into the sand mold, there is a very pronounced tendency for the metal to burn in the sprue and over the entire surface of the casting. Even if the burning is not serious enough to prevent the cast article from being properly finished when removed from the mold, a certain loss of metal, due tooxidation, is inevit-. able, and of course, the cleaner the casting,. the more easily may the finishing operation be carried out.

It has heretofore been proposed to overcome these difficulties specifically in casting magnesium and alloys containing the same by dusting the mold prior to casting the metal with sulphur or equivalent material capable of giving off in contact with the molten metal a vapor which is more easily oxidizable than magnesium. This procedure, however, has the objection that it is obviously difiicult' correctly to gauge the amount of sulphur or equivalent material thus used, and particularly if an excess is applied to the surface either of the mold proper or the core, so much vapor may be generated that some of it becomes entrapped during the period that the metal is solidifying, the result being blowholes or surface shrinks in the casting. Furthermore, the sulphur or equivalent material has'to be applied or dusted onto the mold each time a fresh casting is poured and in any case, the method in question is obviously not applicable where a metal mold is employed,

Application filed January 13, 1926. Serial No. 81,103.- I

because of'the non-porous character of the latter.

I have discovered that where one of the mold parts, specifically the core, is made of a porous material such as sand, superior castings will be produced if such core previously to being assembled in themold is saturated with a suitable neutral .or reducing gas. Accordingly, when the molten metalis poured into-the assembled mold, no air or other harmful gas is given off as such metal comes in contact with the core, and as a result a clean casting free from burns is produced.

To theaccomplishment of the foregoing and related ends, the invention, then, consists of the steps hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail one approved method of carrying out the in vention, such disclosed mode, however. constituting but one of the various ways in which the principle of the invention may be used.

The most convenient gas or vapor wherewith to saturate the cores before they are placed in the molds is sulphur dioxide, this being done by throwing a couple of hands full of sulphur onto the floor of the core oven a short time before the cores are removed therefrom. The length of time will .vary with the size and character of the cores, thirty minutes being found sufficient for those used in casting magnesium pistons of ordinary -size,'although with others fifteen minutes will suflice and several hours will do no harm. The sulphur thus thrown on the hot floor ofv free from burns and without the objectionable use of sulphur in the mold itself.

"gas is still present to produce a clean casting readily oxidizable metals such as magnesium or alloys containing the same. The air in the casting chamber itself is of course readily displaced by the incoming metal, and it is the air remainmg in the pores or interstices of the core that, slowly escaping from such core or other porous mold wall and coming into contact with the still highly heated'metal of the casting, has caused burns and shrinks in such surface.

It will be understood that the present improved method of saturating the cores is not necessarily limited to thus saturating the samein the core oven, but that after the cores have been baked, they may be separately treated by bein placed in a small oven or box in which su phur is kept burning so as to maintain therein the required sulphur dioxide atmosphere. Even though they may have cooled down considerably from the temperature of the oven, the cores-will still contain sufficient sulphur dioxide to yield good cast-- 'ings. Various other materials than sul hur may be employed, for example para dic lorbenz'ol, although this has the disadvantage that the gases generated are more obnoxious than sulphur dioxide, as also naphthalene, carbon tetrachloride, and fuel oil.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and dis-- tinctly claim as my invention 1. A method of casting a readily oxidizable 9. As an article of manufacture, a core havinga surface of porous material, said core being substantially saturated with sulphur dioxide.

10. As an article of manufacture, a core having a surface of porous material substantially saturated with a gas substantially free from uncombined oxygen.

Signed by me, this 5th day of January,

HORACE KELLEY.

metal, which includes the steps of heating and substantially saturatin a porous-surfaced mold part with a su stantially nonoxidizing gas, and casting the molten metal incontact therewith.

2. A method ofcastin a readily oxidizible metal, which includes t e steps of heating lit! and substantially saturating a porous-surfaced mold part with sulphur dioxide, and castirig the molten metal in contact therewith. 3.

method of casting a readily oxidiz- V able metal, which includes baking and substantially saturating a core having a porous surface, with a substantially non-oxidizing gas. 4 v Y 4. A method of ca'stin a readily oxidiz- 'able metal, which inclu es heating a core having a porous" surface in prolonged exposure to a substantially non-oxidizing gaseous atmosphere.

. 5. A method of casting a readily oxidizable metal which includes heating a core havto anatmosphere of sulp 'ur dioxide. 

